Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely non-obvious context: the creditStatus enum semantics with a numeric threshold, and what purchaseOptions implies about downstream payment possibilities (checkout link vs. agent wallet URL). It stops short of stating anything about caching, freshness, or rate limits, so it is strong but not exhaustive.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the primary purpose before the decision guidance. It is dense but each clause earns its place, with only mild redundancy between the enumerated return fields and the later creditStatus explanation.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present the description need not restate return values, yet the semantics it does add (thresholds, purchaseOptions branching) are the parts an agent must act on. Combined with the pre-batch usage guidance, nothing required to call this zero-parameter tool correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes zero parameters, so the baseline of 4 applies; there is nothing for the description to clarify. Its field-level discussion concerns outputs rather than inputs, which the schema does not cover.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description gives a specific verb and resource ('Returns this Prism account's credits and prices') and then enumerates exactly what comes back: credits remaining, per-contract price, Unlimited coverage, and monthly contracts added. Sibling differentiation is implicit in the routing reference to prism_buy_credits, letting an agent separate this read-only status check from the purchase tool.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It states an explicit when-to-use ('check it before a batch'), an interpretation rule with thresholds ('low (2 or fewer left)'), and a conditional hand-off ('when it is low or empty, ask your user before calling prism_buy_credits'). That is a full when/when-not/alternative routing instruction.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.